Answer
In acetonitrile, $CH_{3}CN$, the $CH_{3}$ Carbon is $sp^{3}$ hybridized while the $CN$ Carbon is $sp$ hybridized
Work Step by Step
A carbon is $sp^{3}$ hybridised when it is bonded to 4 other atoms with single bonds.
A carbon atom is $sp$ hybridised when it is bonded to two other atoms (either by 'two double bonds' or by 'one triple and one single bond')
If we represent acetonitrile by $C^{(1)}H_{3}C^{(2)}N$
where $C^{(1)}$ and $C^{(2)}$ are carbon number one and two (for representation purpose only)
The structural Representation of $CH_{3}CN$ will show that the $C^{(1)}$ carbon atom is bonded to 3 Hydrogen atoms and the $C^{(2)}$ carbon atom by single bonds. Thus it is $sp^{3}$ hybridized.
The $C^{(2)}$ carbon atom is bonded to the $C^{(1)}$ carbon atom by a single bond and to the $N$ atom by a triple bond. Thus $C^{(2)}$ is $sp$ hybridized
